PCI - Computer Definition

(2) (Peripheral Component Interconnect) The most widely used hardware interface for connecting peripheral devices. Used in computers of all sizes, PCI provides a shared data path between the CPU and peripheral controllers, such as the network and graphics cards. However, with so many controller circuits built into the motherboard, the need for extra PCI slots in a PC has diminished considerably.
Designed by Intel, Compaq and Digital, the PCI bus first appeared in PCs in 1993 and co-existed with the ISA bus for many years. Later, motherboards had only PCI slots and one specialized slot for the graphics card; first AGP and then PCI Express. Today, motherboards may have a mix of PCI and PCI Express slots or only PCI Express. See PCI Express and Mini PCI.
PCI Shares Interrupts; ISA Did Not
PCI eliminated conflicts that plagued the previous ISA bus architecture, which required a specific hardware interrupt (IRQ) to be assigned to each ISA card. In contrast, the PCI bus architecture shares IRQs. PCs with both ISA and PCI were made for several years, and if there was only one IRQ left after the rest were assigned to ISA cards, all PCI devices could share it.
PCI Slots
PCI runs at 33 MHz or 66 MHz and supports 32 and 64-bit data paths and bus mastering. There are generally three or four slots on the motherboard, and the quantity is based on 10 electrical loads that deal with inductance and capacitance. The PCI chipset uses three, leaving seven for peripheral controllers. A controller on the motherboard uses one load; a plug-in card uses 1.5 loads. A "PCI bridge" connects PCI buses together for more slots. For data rate comparisons of all PCI technologies, see PCI-SIG. See PCI-X, Concurrent PCI, CompactPCI, PXI, PC data buses, PICMG and Sebring ring.

How PCI Is Connected

This illustration shows how the CPU, memory and peripherals are interconnected in a PC.